Structural complexity resulting from pervasive ductile deformation in the Karakoram Shear Zone, Ladakh, NW India

The NW-SE trending, similar to 800 km long, dextral Karakoram Shear Zone bounds southwest Tibet. We investigate an area immediately NW of the Pangong Lake where midcrustal rocks sections of the shear zone are exposed. Here, the dominant shear zone is characterized by dextral mylonitic rocks sheared at amphibolite facies and partly retrogressed to greenschist facies. These rocks define a kilometric, SE plunging inclined-to-recumbent fold in the footwall of a north directed, oblique dextral thrust that exhumed anatectic rocks of the Pangong Range. Argon cooling ages reveal that the Pangong Range cooled from similar to 700 degrees C to 300 degrees C between similar to 18-15 and similar to 10 Ma, contemporaneously with overthrusting. Toward the SE, closer to the Pangong Lake, this kilometric fold is rotated from its NW-SE trend to an E-W trend, and the sense of shear changes to sinistral, with a broadly north directed thrusting component. The documented structures contradict predictions of normal movement in this area derived from considerations of rigid block behavior of the crust and support the interpretation that the system records dextral transpression. Thrusting and exhumation of the deeper and hot rocks exposed in the Pangong Range, folding of the thrust footwall, and the development of a sinistral E-W trending shear zone are all compatible with transpression caused by a northward push by a rigid indenter such as the Ladakh Batholith. Citation: McCarthy, M. R., and R. F. Weinberg (2010), Structural complexity resulting from pervasive ductile deformation in the Karakoram Shear Zone, Ladakh, NW India, Tectonics, 29, TC3004, doi:10.1029/2008TC002354.